A spring source gushing forth inside a cave

The name "Hashiriyu" (literally "running water") acquired its name from the way the hot water gushes out from the mountains and races down, plunging to the coast. Discovered about 1,300 years ago, this type of spring with its source located in a horizontal tunnel is very rare even in Japan. The "Hashiriyu" of Izusan Onsen is one of "the three oldest and largest hot springs in Japan" along with Dogo Onsen in Ehime and Arima Onsen in Hyogo. Formerly this place was worshiped as a sacred hot spring of Izusan Shrine, and still now, hot spring water of about 70 °C wells up in the cave.